Method of and apparatus for growing crystals



Oct. 16, 1951 F. BALDUzzl METHOD OF AND APPARATUS FOR GROWING CRYSTALS Filed July 6. 1948 Patented Oct. 16, 1951 METHOD OF AND APPARATUS FOR GROWING CRYSTALS Franco Balduzzi, Zurich, Switzerland, assignor to Patelhold Patentverwertungs- & Elektro- Holding A.-G., Glarus, Switzerland Application July 6, 1948, Serial No. 37,202 In Switzerland July 12, 1947 12 Claims.

This invention relates to crystals and in particular to an improved apparatus for controlling the temperature of the solution in which the crystals are grown within extremely narrow limits.

Generally speaking, crystals are grown by immersing a crystal nucleus in a saturated solution of the crystalline substance and either gradually reducing the temperature of the solution or gradually evaporating the solvent from the solution over an extended period which often runs into weeks. In either method it is most essential that accurate control of the solution temperature be maintained to the end that temperature fluctuations be confined within exceedingly narrow limits. When the reduction-intemperature method is used, the decrease in temperature must take place very slowly, being of the order of 0.1 of a degree per day, and during periods of several hours or so, the fluctuation in temperature from the prescribed value must be held within 0.01 of a degree for otherwise the growing crystal will suffer a loss in quality becoming cloudy, or porous in certain places or even cracking. The same requisites as to temperature control apply when crystal culture is carried on according to the evaporation method.

In apparatus heretofore developed for growing the crystals, it has been the practice to place a vessel containing the solution of the crystalline substance in a liquid bath that is maintained at the desired temperature by means of an electrical heating element, the latter being immersed directly in the bath or in the form of a hot plate placed outside of the tank containing the bath liquid, and in good heat conductive relation with the walls thereof, and to control the operation cf the electric heater by means of the usual thermostatic device immersed in the bath. This type of apparatus, however, hasY proven not entirely satisfactory and the difliculty stems from a high thermal inertia condition brought about by the relatively high heat capacity of the liquid bath and of the heating element and the Vessel walls as well as the crystalline solution itself. Elforts have been made to counteract this disadvantage through use of Various types of stabilizing controls such as thermal elements with compensation bridges, and photocells with amplifiers, but these are highly complicated and in general quite expensive.

It has also been proposed to eliminate the liquid both for the crystalline'solution and heat y the latter directly. This reduces the overall thermal inertia of the system, but there are other disadvantages to this method. If the heating element is placed directly in the crystalline solution, it must be provided with a protective coating that will not react chemically with the solutionand satisfactory coatings have been difiicult to nd for use with solutions containing phosphorous. Furthermore, the heating effect of a heater element immersed directly in the crystalline solution is highly localized, being restricted to that part of the solution in the direct vicinity of the heater, and hence the entire body of the solution must be kept in rather rapid and continuous state of motion in order to maintain the temperature anywhere near uniform.

Furthermore all of the above-mentioned types of apparatus have the additional disadvantage that the surface layer of the solution, even when covered by a lighter liquid protective layer such as oil, always has a lower temperature than the remainder of the solution, which makes it easily possible for undesirable new nuclei to separate out of the solution at the boundary layer while the crystal nucleus under culture is being grown. These new nuclei gradually sink to the bottom and proceed to grow either by themselves, or what is even worse, grow together with the crystal under culture thus leading to harmful twin formations.

The general object of this invention is to provide an improved apparatus for heating and controlling the temperature of the saturated solution containing a crystal under culture which features a low Vthermal inertia. More specically an object of the invention is to provide for heating the solution -by means of infra red radia-v tion. Another object is to provide for automatically lowering the temperature of the saturated solution.

The foregoing as Well as other objects and advantages to be derived from the invention will become more apparent from the following detailed description of preferred constructional embodiments when considered with the accompanying drawings. As to the latter:

Fig. 1 is a diagrammatic View illustrating one spacial arrangement for the infra red radiators together with the automatic electric control therefor shown schematically; and

Fig. 2 is a view similar to Fig. 1 illustrating a somewhat dilferent arrangement for the infra red radiator and a different means for controlling its operation.

Referring now to Fig. l, the apparatus is seen lto include a tank I which for chemical considerations is preferably made of glass. The saturated solution of the crystalline substance in the tank is indicated at 2, and the crystal being grown in the solution is designated 3. Preferably, solution 2 is covered with a layer of a lighter liquid 4 which will pass the infra red radiations practically without any absorptiony of heat.v The covering layer 4 should be such as not to react chemically with the crystalline solution and the vapor pressure of the liquid cover layer 4 should not exceed 10% of the vapor pressure of the solution 2 at the required culture temperature. Aliphatic oils have been found to be especially satisfactory for this purpose, since they exhibit only a slight heat absorption factor in the infra-red band and have a low vapor pressure at the culture temperature, the latter usually being from 20 to 100 centigrade. The layer of oil 4 is preferably about 1/2 to 1 centimeter in thickness.

For heating the solution 2, infra red radiators are employed, and in the Fig. 1 construction two such filament type radiators 5 and 6 are shown above tank I and at opposite ends of the tank. Reectors 5a, 6a placed behind the filaments help direct the rays, and preferably each filamentreflector unit is so designed and oriented that the infra red beam produced thereby will extend over the entire surface area of the solution. Infra red bulbs with integral reflectors of the type already commercially available are preferably used, but use can also be made of a non-enclosed infra red heater coil wound on a ceramic base of the type now used commercially in infra red drying ovens, with separate reflectors.

The cross sectional area of tank I and the depth of the solution 2 are preferably s0 chosen that not more than 1% of the infra red radiation sent into the tank from the lamps 5, 6 is still present at the tank bottom. By so doing, the heating effect is more evenly distributed over the Whole volume of the solution and hence helps to prevent the formation of temperature strata or layers which are undesirable for reasons already explained. The depth of the solution will of course depend upon the particular absorption characteristics of the solution 2 and cover layer 4 and hence will vary dependent upon the particular liquids used. i,

While the temperature of the solution will be substantially uniform throughout, it is preferable to keep the solution in a rather slow state of motion. For this purpose, a propeller type agitator 1 submerged in the solution and driven at a rather slow speed from an electric motor 'la can be used. Agitation of solution 2 also helps to prevent formation of temperature layers and weakening of the solution in the vicinity of the crystal 3.

Alternatively, the agitator unit 'I can be dispensed with and substantially the `same results obtained by moving the crystal in the solution. This latter arrangement is described hereinafter in a modified construction and has the advantage of eliminating at least one object in the solution extraneous to the crystal, for generally speaking, the smaller the number of accessories immersed in the solution, the more ideal does the culture apparatus become.

The control over the infra red radiators 5, 6 in the Fig. 1 construction is essentially an off-on arrangement, effectedthrough the use of a mercury typek thermometer-switch unit. 8 immersed in the solution, a relay 9 controlled by it, and a power relay I2 controlled by the contacts of relay 9 for switching radiators 5, 6 on and off with respect to terminals I3 of a source of power supply.

'Ihe thermometer-switch unit 8 includes a lower bulbous section I4, and an upper capillary tube section I5 containing a contact wire I 6 that is progressively lowered with time as the culture proceeds. Lowering of wire I6 is effective to gradually reduce the temperature of the solution and may be effected by the use of a clockwork drive II as indicated on the drawing, or by some other generally familiar means such as impulse relays, servomotors, etc.

Thermometer-switch unit 8 is connected via conductor I8 in contact with the mercury I9 and iconductor 20 in contact with wire I6 in series relation with the winding 9a of relay 9 to power source terminals 23 and effects a closure of relay contacts 9b each time the mercury rises in the capillary I5 to a point where it makes Contact with the lower end of wire I6.

Relay contacts 9b are in turn connected in series with winding I2'a of the heavy duty relay I2 to the power source terminals 23 and the relay contacts I2b. are arranged to open wheneven relay winding I-2a is energized by a closure of relay contacts 9b. Opening of relay contacts I2b opens the energizing circuit between the power source terminals I3 and the infra red radiators 5 and 6.

The operation of the Fig. l control should now be obvious. Whenever the temperature of the solution is such as to call for more heat, as evidencedv by a gap between the mercury column I9 and contact Wire I5, to restore the solution temperature to the proper level, the infra red radiators 5, 6 will be turned on; and conversely when the solution temperature is such as to order less heat, radiators 5 and 6- will be turned oli.

In the drawings, an instant is depicted at which solution 2 has dropped slightly below the required temperature level. Under such conditions, relay winding 9a is deenergized and hence relay contacts 9b are open which means that Winding I2a of relay I2 will likewise be in a deenergized state leaving relay contact I2b closed; under such conditions, radiators 5, 6 will be connected to the source terminals I3. As the infra red energy penetrates the solution 2, the latter of course is heated by it causing the mercury I9 to rise in capillary I5 until it reaches Contact wire I6. When this occurs, both relays 9 and I2 become energized causing the radiators 5, 6 to be turned off as relay contacts I 2b open. The radiation ceases immediately, and as soon as solution 2 cools down again where contact between mercury I9 and wire I6 is broken, the radiators 5, 6 are turned on again.

With the Fig. 1 system, it has been found that exceedingly accurate and reliable temperature control (with temperature fluctuations maintained within 0.01 of a degree centigrade at a room temperature of about 18 centigrade and a solution temperature of about 25 to 50 degrees centigrade) can be obtained by using an infra red radiation factor of to 90 watts per liter of saturated solution of the crystalline material. Using such arrangement, the infra red, radiators 5, 6 will then be switched in for about one-half to one second about every four to six second period. When the apparatus is operated in a room at normal ambient temperature, it has been found that the walls of tank I do not have to be insulated from the surrounding air even though the latter varies i5 degrees centigrade Within a span of a few hours. Special measures for temperature regulation of the culture rooms are therefore unnecessary in most cases.

Indeed, under certain very favorable conditions, the temperature of the solution using the Fig. 1 apparatus has been maintained constant within 0.002 of a degree centigrade as compared with the prior known systems where iiuctuations in temperature of the order of 0.1 to 0.3 a degree centigrade were not unusual.

If an even more constant temperature is desired, which will onlyrseldom be the case for growing crystals, thermostats more sensitive than the mercury type 8 can be used for controlling the on-off operation of the infra red radiators 5 and 6. Examples of these finer controls are toluol or gas thermometers with mercury laments in which case a temperature constancy within 0.001 of a degree centigrade or even better can be expected when used in combination with the low thermal inertia infra red type of heat source.

It is obvious that the number of infra red radiators is not critical. While two are illustrated in Fig. 1, more than two can be utilized and an arrangement of four such radiators placed above and grouped symmetrically about the axis of rotation of a circular vessel containing the 4saturated solution of crystalline material is particularly advantageous since it affords a more uniform radiation -of the surface of the solution.

In Fig. 2, I have illustrated a modied construction which is particularly adapted for use where crystal culture requires comparatively high solution temperatures, i. e. temperatures above 50 or 60 degrees centigrade. This construction also features continuously energized infra red radiators with a screen for controlling passage of infra red radiation into the solution, means for moving the crystal about in the solution as distinguished from the solution agitator employed in the Fig. l construction, and a resistance bridge type of thermostatic control.

Referring now to Fig. 2, the tank for the solution 24 is denoted by numeral 25 and the surface liquid layer of aliphatic oil is designated 26. The crystal 21 under culture, instead of being suspended in a stationary manner as is done in the Fig. 1 arrangement, is suspended from a rod 28 extending laterally of and `secured to a vertical shaft 29 that is rotated on its axis by an electric motor 3l).

The thermostatic control unit which is a resistance bridge 32 as distinguished from the mercury thermometer unit of Fig. 1 includes a temperature sensitive branch 33 immersed in the solution 24 and three `other branches 34-36. Branches 34 and 35 are relatively fixed in resistance value once properly adjusted, but the resistance of branch 36 is Varied as a function of time by means of a clockwork 37 in order to alter the bridge balance with time so that the temperature of the solution will drop at the desired rate as crystal culture proceeds.

Power for energizing the bridge is applied to one set of bridge diagonals 32a and the bridge output is fed from the other set of bridge diagonals 32h into the grid circuit of an electronic amplifier 38 of conventional design. The control is so arranged that unbalance of the bridge 32 in the direction caused by a drop in temperature of solution 24 below the required level effects a decrease in the `output current from amplier 38 from a predetermined amplitude, and conversely a rise in solution temperature above such level eiiects an increase in the amplier output current.

The output fromy amplifier 38 is applied to winding 39a of solenoid 39 and the armature 39'bfof the latter is attached to one end of a slide or screen 40 containing an aperture 4| by which infra red radiation from radiator 42 intothe solution 24 is controlled. Radiator 42 energized continuously from power source terminals 43 is of the same type as used in the Fig. 1 arrangement 'and is located centrally above the tank 25. A

spring 44 is secured to the opposite side of slide 40 and its direction of pull with respect to slide 40 is of course opposite to that exerted upon the other side of the slide by the solenoid armature 39h. Hence if the solution temperature rises above the prescribed level, the increase in current in solenoid winding 39a is reflected by an increase in the force applied to the right byarm-ature 39h and causes slide 40 to take such a position as will screen off at least some of the infra red radiation from the solution 24. On the other hand, should the solution temperature fall below the prescribed level, the current in solenoid winding 39a will decrease thus decreasing the pull of larmature 39h whereupon the force exerted by spring 44 dominates and causes slide 40 to take such a position that more of the infra red radiation from lamp 42 will pass through the aperture 4I in the slide. The latter condition is depicted in Fig. 2 where it will be noted that the aperture 4| occupies such a position that the entire surfaceof the solution 24 is exposed to the infra red radiation from lamp 42.

The Fig. 2 apparatus is also designed to be operated at a relatively high solution temperature i. e. above 50 to 60 degrees centigrade and hence tank 25, lamp 42 and the other necessary component parts are enclosed by a housing 45 the walls of which are either built directly from insulating material, or suitably insulated with such material. Use of the housing 45 cuts down on heat loss to the surrounding Iair and therefore prevents the temperature of the culture rooms from becoming unbearably hot, and this is especially of advantage when a numberof crystal cultures are being carried on continuously in the same room.

The air within housing 45 should preferably be kept constant withina departure range of from 0.5 to 2.0 degrees and this can be accomplished through use of a comparatively simple temperature regulator such as a bimetallic thermostatic unit 46 placed within the housing that controls an auxiliary electric heater unit 41 also in housing 45 that is supplied from electric power terminals 48. Use of the housing around the tank 25 also further improves the temperature regulation of the solution 24 making it possible to narrow the temperature fluctuation to even finer limits.

If desired, a similarly arranged housing can be incorporated in the Fig, 1 construction. Moreover it is obvious that a screen type cut-olf control for the infra red radiation can be substituted for the relay arrangement in Fig. 1 where radiation control is obtained by alternately switching the energizing current to the radiators on and off. The screen type cut-olf has the advantage that the radiators remain energized continuously which is conducive to a longer lamp life since-it is common knowledge that the life of a. lamp filament is materially shortened if the filament current is repeatedly switched on and olf.

Reverting to the Fig. 2 arrangement, itis of course possible to use more th-an the one infra red radiator there illustrated. A plurality of such radiators using a single screen with a separate aperture for each radiator might in fact be quite desirable in the interest ofV more 'uniform radiation of the solution surface for in suchcase they would be arranged so that the radiation from each would cover a separate part of the surface of the solution and hence partial screening of the several radiated beams would still leaveA the solution surface substantially uniformly radiated, but to a lesser intensity. In other words, screening oli' of the radiation would not leave any single large section of the solution surface unradiated as would be the case when but a single radiator as shown in Fig. 2 is used and screening takes place progressively from one side of the tank to the other leaving about one half of the solution surface entirely screened olf and the other half entirely radiated.

In conclusion, it will be evident that the improved apparatus for crystal culture in the various embodiments which have been described offers distinct advantages over those which have been previously designed for this purpose. The dominant feature is of course the novel and improved arrangement for more accurately controlling the temperature of the crystalline solution and this is highlighted by the use .and control of infra red radiators as the source of heat. As explained in the opening part of the description, this type of radiation has a very low thermal inertia and can be cut oi abruptly as compared with the other types of heaters formerly used and which because of their large heat storage capacity exhibit a high thermal inertia after cut-ot that leads to an undesirable temperature overide or "hunting effect in the temperature control that makes close regulation impossible.

Furthermore, while the illustrated embodiments of the invention are preferred, these by no means exhaust the design possibilities and hence various changes in the construction and arrangement of components may be effected by others without departing from the spirit and scope of the invention as dened in the' appended claims.

I claim:

1. Apparatus for growing crystals immersed in a saturated solution of the crystalline substance comprising a tank for receiving a body of the solution, an electrically energized radiator of heat having a low thermal inertia and a high infra red wave energy output, said heat radiator being so located with respect to said body of solution that the latter is heated substantially solely by said infra red wave energy, temperature responsive means including a temperature sensitive element in the tank adapted to be immersed in the solution, and means controlled by said temperature responsive means for regulating the amount of said wave energy reaching the solution from said radiator.

2. Apparatus for growing crystals as defined in claim 1 wherein said temperature sensitiveA element is comprised. of a resistance element formingr one branch. of an electrical bridge, said wave energy regulating means is actuated in accordance with the bridge output, and said bridge includes means for adjusting the resistance value of another branch thereof in accordance with time.

3. Apparatus for growing crystals as dened in claim 1 wherein said temperature sensitive element is comprised of a liquid thermometer type switch, one contact of which is constituted by the liquid column in the capillary section of the thermometer and the other contact by a member slidable in said capillary section, and means for adjusting the position of said slidable member in accordance with time.

4. Apparatus for growing crystals as defined in claim 1 wherein the means for regulating said wave energy is comprised of switching means controlling the circuit connections between said electrically energized radiator and its source of power.

5. Apparatus for growing crystals as dened in claim-1 and which further includes a housing enclosing said tank and infra red wave energy radiator, and means for maintaining the temperature of the space within said housing substantially constant.

6. Apparatus for growing crystals immersed in a saturated solution of the crystalline substance comprising a. tank for the solution, an infra red wave energy radiator so positioned as to direct such energy into and heat the solution substantially solely by radiation, a screen placed between said radiator and the interior of said tank, said screen being movable into and out of the path of said infra red wave energy to decrease or increase, respectively, the amount thereof reaching the solution, temperature responsive means in said tank and adapted to be immersed in the solution, and means actuated by said temperature responsive means for controlling the movement of said screen.

7. Apparatus for growing crystals as defined in claim 6 wherein said screen is constituted by an apertured slide member positioned for movement in a plane transversely of the axis of said infra red wave energy.

8. The method of growing crystals immersed in a predetermined volume of solution of the crystalline substance which comprises the steps of heating the solution substantially solely by radiation from a source'of infra red energy situated above the surface of the solution, the depth of the solution being so related to the intensity of the energy source that at the bottom of the solution only a small fraction of the order of 1% of the total infra red energy radiated into the top surfaceof the solution remains, and controlling said radiation in accordance with the temperature of the solution.

9.v The method of growing crystals immersed in a saturated solution of the crystalline substance which comprises the steps of heating the solution substantially solely by radiation from a source of infra red wave energy, the radiation factor being within the limits of sixty to ninety watts of energy per liter of the solution, and controlling the radiation from said energy source in accordance with the temperature of the solution.

10. The method of growing a crystal which comprises the steps of immersing the crystal in a saturated solution of the crystalline substance, covering the surface of such solution with a less dense layer of a liquid, said covering liquid being permeable to infra red wave energy but chemically inert with respect to the solution and having a vapor pressure not exceeding 10% of that of the solution at the crystal culture temperature, heating the solution substantially solely by radiation from a source of infra red Wave energy located above said covering liquid, and controlling the radiation in accordance with the temperature of the solution.

l1. The method of growing a crystal as defined in claim 10 wherein said covering liquid is an aliphatic oil.

12. The method of growing a crystal immersed in a saturated solution of the crystalline substance which comprises the steps of irradiating the solution with infra red wave energy to heat the same and controlling said irradiation to establish a temporal temperature gradiant in said solution.

FRANCO BALDUZZI.

REFERENCES CITED The following references are of record in the 10 le of this patent:

Number Number 10 UNITED STATES PATENTS Name Date Schimmel July 6, 1915 Newcomb July 9, 1929 Chormann Oct. 7, 1930 Kjellgren May 2, 1933 Selvig May 4, 1943 Gille Jan. 2, 1945 Kjellgren Oct. 4, 1949 FOREIGN PATENTS Country Date Australia May 9, 1930 

1. APPARATUS FOR GROWING CRYSTALS IMMERSED IN A SATURATED SOLUTION OF THE CRYSTALLINE SUBSTANCE COMPRISING A TANK FOR RECEIVING A BODY OF THE SOLUTION, AN ELECTRICALLY ENERGIZED RADIATOR OF HEAT HAVING A LOW THERMAL INERTIA AND HIGH INFRA RED WAVE ENERGY OUTPUT, SAID HEAT RADIATOR BEING SO LOCATED WITH RESPECT TO SAID BODY OF SOLUTION THAT THE LATTER IS HEATED SUBSTANTIALLY SOLELY BY SAID INFRA RED WAVE ENERGY, TEMPERATURE SENSITIVE ELEMENT MEANS INCLUDING A TEMPERATURE SENSITIVE ELEMENT IN THE TANK ADAPTED TO BE IMMERSED IN THE SOLUTION, AND MEANS CONTROLLED BY SAID TEMPERATURE RESPONSIVE MEANS FOR REGULATING THE AMOUNT OF SAID WAVE ENERGY REACHING THE SOLUTION FROM SAID RADIATOR.
 8. THE METHOD OF GROWING CRYSTALS IMMERSED IN PREDETERMINED VOLUME OF SOLUTION OF CRYSTALLINE SUBSTANCE WHICH COMPRISES THE STEPS OF HEATING THE SOLUTION SUBSTANTIALLY SOLELY BY RADIATION FROM A SOURCE OF INFRA RED ENERGY SITUATED ABOVE THE SURFACE OF THE SOLUTION, THE DEPTH OF THE SOLUTION BEING SO RELATED THE INTENSITY OF THE ENERGY SOURCE THAT AT THE BOTTOM OF THE SOLUTION ONLY A SMALL FRACTION OF THE ORDER OF 1% OF THE TOTAL INFRA RED ENERGY RADIATED INTO THE TOP SURFACE OF THE SOLUTION REMAINS, AND CONTROLLING SAID RADIATION IN ACCORDANCE WITH THE TEMPERATURE OF THE SOLUTION. 